1. Field of the Invention
The present disclosure relates generally to wireless communication, and more specifically for reference signal (RS) sequence initialization for wireless communication systems.
2. Relevant Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink, DL) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink, UL) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
In addition, multi-user MIMO (MU-MIMO) systems are provided that allow an access point (or other wireless device) to simultaneously transmit to multiple UEs (or other wireless devices) using MIMO over a single frequency band. In this regard, access points can transmit UE specific reference signals (RS) to the UEs for demodulating data transmitted simultaneously in one or more signals in the frequency band. In LTE Release 8 (Rel-8) for single-layer beamforming, UE RS sequences are defined in terms of bandwidth of one or more resource blocks of a corresponding downlink transmission. In addition, pseudo-random sequences for the UE RS are generated according to a UE-specific identifier.